The Elizabethans were the raunchiest group of writers that I've ever had the joy to read. They just hide it all in double entendres, so you have to have the dirty mind of a twelve-year-old and the background of an academic to get them. If you want to read what's (to me, anyway) the funniest line-by-line analysis of this sonnet, go here. It cracks me up to have this really academic analysis talking about 'pricks' and puns on 'conscience' really meaning 'cunt-science'. The poor academic sounds entirely confused and a bit put out by the whole thing.
But then again, I have the dirty mind of a twelve-year-old. *huge grin*